Borderline personality disorder (BPD) and deliberate self-harm are clinically important conditions for which additional economically and clinically feasible interventions are needed. Literature on both the emotion regulating and experientially avoidant function of self-harm and the role of emotional dysfunction in BPD provided the rationale for developing a group intervention targeting emotion dysregulation among self-harming women with BPD. This study provides preliminary data on the efficacy of this new, 14-week, emotion regulation group intervention, designed to teach self-harming women with BPD more adaptive ways of responding to their emotions so as to reduce the frequency of their self-harm behavior. Participants were matched on level of emotion dysregulation and lifetime frequency of self-harm and randomly assigned to receive this group in addition to their current outpatient therapy (N = 12), or to continue with their current outpatient therapy alone for 14 weeks (N = 10). Results indicate that the group intervention had positive effects on self-harm, emotion dysregulation, experiential avoidance, and BPD-specific symptoms, as well as symptoms of depression, anxiety, and stress. Participants in the group treatment condition evidenced significant changes over time on all measures, and reached normative levels of functioning on most. While these preliminary results are promising, the study’s limitations require their replication in a larger-scale randomized controlled trial.